1. Field of the Invention
The present invention relates to a sheet transport device having a toothed wheel mounted on a rotary shaft of transport means for transporting a sheet. The sheet transport device is applied to a recording apparatus such as a printer, copying machine, word processor, personal computer, and facsimile, etc.
2. Description of the Related Art
In some conventional recording apparatuses, a transport roller is employed as transport means integrally provided with a rotary shaft for transporting a sheet, and a toothed wheel (referred to as a xe2x80x9cgearxe2x80x9d hereinafter) for transmitting torque to the transport roller is mounted on the transport roller. That type of recording apparatus has hitherto been constructed such that (1) no gear cover is provided for a gear on the transport roller, or (2) a gear cover is provided to protect the entirety the transmission gears for transmitting torque from a driving source to the transport roller, including the gear on the transport roller, as disclosed in Japanese Patent Laid-Open No. 5-289280.
In those recording apparatuses, because an effect of gear accuracy upon sheet transport accuracy cannot be moderated through a speed reduction, the gear mounted on the transport roller and serving as a final gear is designed to have a large diameter. Thus, the sheet transport accuracy is improved by setting the number of teeth of the gear mounted on the transport roller as large as possible.
However, the conventional recording apparatuses described above have the following problems:
(1) In the construction where no gear cover is provided for the gear on the transport roller, when the transport roller including the gear on the transport roller is assembled into a frame of an apparatus body, careful attention is required so that the gear on the transport roller will not contact surrounding parts and damage them. Accordingly, the efficiency in assembly work has been poor.
Further, even after the transport roller including the gear mounted thereon has been assembled into the frame, when the frame is assembled into an outer housing or when an upper case is mounted to the frame, careful attention is also required so that the outer housing or the upper case will not contact the gear on the transport roller and damage the same. Accordingly, the efficiency in assembly work has been poor in that point as well.
(2) In the construction where a gear cover is provided to protect the entirety of the transmission gears, a large space for the gear cover is required and the size of the apparatus is enlarged. Also, providing the gear cover necessarily pushes up a production cost.
Moreover, in any of the above cases (1) and (2), it has been difficult to move and store the transport roller as one unit that is in a condition where the gear is mounted on the transport roller. This difficulty has been inconvenient in handling the transport roller.
The present invention has been accomplished to solve the above-mentioned problems in the related art. An object of the present invention is to provide a sheet transport device and a recording apparatus in which transport means is constructed as a unit including a first gear and a protective member both integrally mounted on a rotary shaft, thereby ensuring easy handling, an inexpensive cost, good efficiency of assembly work and high reliability.
To achieve the above object, the present invention provides a sheet transport device comprising a transport roller having a rotary shaft rotatable about an axis and transporting a sheet with rotation of the rotary shaft, and a first gear fixedly coupled onto the rotary shaft of the transport roller and transmitting torque from a driving source to the rotary shaft, wherein the sheet transport device further comprises a protective member fixed to the rotary shaft and protecting teeth of the first gear.
With the above features, the transport roller can be constructed as a unit including the first gear and the protective member both integrally mounted on the rotary shaft (transport roller itself). In the unitized transport roller (transport roller unit), the teeth of the first gear are protected by the protective member. Therefore, the transport roller can be easily handled, simply assembled into an apparatus body, and assembled with higher efficiency. Further, the protective member protects only the first gear on the rotary shaft, and hence can be provided at an inexpensive cost.
Preferably, the first gear is fixed to one end of the rotary shaft, and the protective member is provided substantially in the form of an umbrella covering the first gear from the outer side of the one end of the rotary shaft.
With the above features, the protective member can protect the outer side of the one end of the rotary shaft, i.e., the first gear fixed to the one end and tending to be easily damaged.
Preferably, the protective member prevents the first gear from slipping off of the rotary shaft.
With the above feature, an additional part for preventing slip-off of the first gear is no longer required, an increase in the number of parts of the device can be avoided, and the device can be constructed at an inexpensive cost.
Preferably, the first gear includes a tubular fixing portion fixedly coupled to the rotary shaft, and the protective member has a fitting hole fitted to a tubular outer circumference of the tubular fixing portion, thereby positioning the protective member in a circumferential direction.
With the above features, since positioning of the protective member in the circumferential direction is made by fitting it between the tubular fixing portion and the fitting hole, the device size is not increased, and the device can be provided in a smaller space.
Preferably, a groove is formed in the tubular fixing portion of the first gear, a lug projecting radially inward is provided at an inner circumference of the fitting hole formed in the protective member, and the lug of the protective member is fitted in the groove of the tubular fixing portion to prevent the first gear from rotating relative to the transport roller.
With the above features, an additional part for preventing the first gear from rotating relative to the transport roller is no longer required, an increase in the number of parts of the device can be avoided, and the device can be constructed at an inexpensive cost.
Preferably, the protective member protects a second gear as well, which meshes with the first gear.
With the above feature, the teeth of the first gear can be protected with sufficient reliability. It is therefore easier to handle the transport roller which is constructed as a unit including the first gear and the protective member both integrally mounted on the rotary shaft.
A recording apparatus according to the present invention comprises the sheet transport device described above, and a recording unit for carrying out recording in accordance with image information on a sheet transported through the recording unit.
With the above features, since the transport roller can be easily handled in the form of a unit including the first gear and the protective member both integrally mounted on the rotary shaft, the efficiency of assembly work of the apparatus can be improved, a time required for the assembly work is cut down, and the apparatus can be manufactured at a relatively inexpensive cost.
Preferably, the recording unit is an ink jet recording unit.